JP4133657B2 - X-ray fluoroscope for precision measurement - Google Patents

Description

  The present invention relates to an X-ray fluoroscopic apparatus used for industrial measurement, nondestructive inspection such as inspection of defects inside articles and inspection of internal structures, and in particular, X for precise measurement capable of precise dimension measurement from a fluoroscopic image. The present invention relates to a fluoroscopic apparatus.

  In an X-ray fluoroscopy apparatus, generally, a sample table movable in a three-dimensional direction is arranged between an X-ray tube and an X-ray detector, and X-rays are emitted with a fluoroscopic object placed on the sample table. By irradiating, the X-ray transmitted through the fluoroscopic object is detected by the X-ray detector, and the X-ray fluoroscopic image of the fluoroscopic object is displayed on the display screen using the output of the X-ray detector. .

  In this type of fluoroscopic apparatus, a geometrical shape is usually determined by the distance formed between the focal point of the X-ray tube and the X-ray detector (image receiving surface) and the distance formed between the focal point of the X-ray tube and the fluoroscopic object. The perspective magnification, in other words, the imaging magnification of the fluoroscopic object on the image receiving surface of the X-ray detector is determined. The fluoroscopic magnification (imaging magnification), which is the ratio between the size of the X-ray fluoroscopic image displayed on the display screen and the actual size of the fluoroscopic object, is determined by the X-ray detector. When an optical system such as a lens is incorporated in the X-ray detector, the relationship between the pixel and the pixel of the display device must be determined in consideration of the magnification ratio of the image by the optical system.

  Therefore, conventionally, in order to obtain a fluoroscopic magnification including all of these elements, a reference sample having a known dimension called a microchart or the like is arranged on a sample table, and an X-ray fluoroscopic image of the reference sample is provided. Is displayed on the display, the actual size per pixel of the display, that is, the spatial calibration value is obtained. If this spatial calibration value is obtained, a bar called a measurement bar tool that can be moved and expanded by operating the mouse or the like is displayed on the screen of the display unit, and the bar is displayed between any two points on the screen. Software that can automatically calculate and display the actual dimensions between the two points by moving and expanding and contracting so as to point to the bar is often used.

  In order to accurately display the actual dimensions between any two points on the X-ray fluoroscopic image using the spatial calibration values as described above, it is natural that the same perspective magnification as when the spatial calibration values are obtained. It is necessary to display an X-ray fluoroscopic image. Therefore, after performing spatial calibration under a certain magnification ratio, if you want to know the dimensions of any part by moving the field of view to the place you want to observe, if you change the magnification ratio, the spatial calibration obtained by the previous calibration Since dimensional measurement using values becomes impossible, spatial calibration must be performed again at the enlargement ratio. In addition, when performing spatial calibration again, there are cases where the size of the reference sample determined as the calibration standard is too small or too large for the enlargement ratio.

  Furthermore, in this type of conventional fluoroscopic apparatus, since the dimension in the X-ray optical axis direction between the site of interest inside the fluoroscopic object and the surface of the sample table is unknown, the sample table, X-ray detector, or X-ray Strictly speaking, the actual dimension of the target site cannot be measured with high accuracy without moving the tube at all in the X-ray optical axis direction, and thus changing the apparent perspective magnification from the time of spatial calibration. .

  That is, the spatial calibration value is determined by the distance between the focal position of the X-ray tube and the image receiving surface of the X-ray detector and the distance between the focal position of the X-ray tube and the reference sample. It functions effectively when the imaging magnification is constant, and if this imaging magnification is different, an accurate actual dimension cannot be obtained. Since the distance from the surface of the sample table to the X-ray optical axis direction is usually unknown when the fluoroscopic object is placed on the sample table, the site of interest inside the fluoroscopic object is the focus of the X-ray tube. The distance from the position is unknown, and therefore the imaging magnification is different from that at the time of spatial calibration using the reference sample without changing the apparent perspective magnification.

Conventionally, as a method for obtaining an accurate perspective enlargement ratio of a target region inside the fluoroscopic object, after specifying the target region in a state where an X-ray fluoroscopic image is displayed by placing the fluoroscopic object on the sample table, the sample table Is moved by a predetermined amount δ in the direction orthogonal to the X-ray optical axis, and the amount Δ of the movement of the image of the target region on the display screen by the movement is obtained by image processing, and the movement of the target region on the screen There has been proposed an X-ray fluoroscopic apparatus that calculates a fluoroscopic magnification by Δ / δ from an amount Δ and a movement amount δ of a sample table (see Patent Document 1).
JP 2002-243663 A

  However, even if the above-described proposed technique is used to accurately know the perspective magnification of the site of interest, the screen is displayed using this technique, the spatial calibration value obtained by imaging the reference sample and the measurement bar tool described above. Since it functions independently of the software that automatically calculates and displays the actual dimensions between any two points specified above, the actual dimensions between any two points on the fluoroscopic image can be easily and It cannot be measured with high accuracy.

  The present invention has been made in view of such circumstances, and after performing spatial calibration using a reference sample, the distance from the sample table surface inside the fluoroscopic object is unknown even if the fluoroscopic magnification is changed. An object of the present invention is to provide an X-ray fluoroscopy device for precision measurement that can automatically calculate and display the actual dimensions with high accuracy using a spatial calibration value from the screen.

In order to achieve the above object, an X-ray fluoroscopic apparatus for precision measurement according to the present invention includes an X-ray tube, a sample table having a function of moving in a three-dimensional direction, and an X-ray tube sandwiching the sample table. An X-ray detector disposed opposite to the X-ray detector, a tilting mechanism for tilting the X-ray detector around the focal point of the X-ray tube, and an X-ray fluoroscopic image based on pixel information from the X-ray detector Spatial calibration for calculating a spatial calibration value from an X-ray fluoroscopic image of a reference sample with a known dimension placed at a position where the distance in the X-ray optical axis direction with respect to the surface of the sample table is known. In the precision measurement X-ray fluoroscopy device provided with the value calculation means, the storage means for storing the spatial calibration value together with the fluoroscopic magnification of the X-ray fluoroscopic image of the reference sample used for calculating the spatial calibration value; The distance from the surface of the sample table exists at the road position Includes a site of interest perspective enlargement ratio calculation means for exiting calculate the perspective magnification region of interest of the object of fluoroscopy that, when calculating the perspective magnification attention site by the attention site fluoroscopic magnification ratio calculating means, the calculated value and the The spatial calibration value is automatically changed based on the ratio with the perspective magnification stored in the storage means, and the storage means is determined based on the spatial calibration value after the change and the calculated perspective magnification of the target region. A spatial calibration value / perspective magnification update means for updating the contents of the image, and the attention site fluoroscopic magnification calculation means, when the X-ray detector is tilted by a predetermined angle by the tilt mechanism, The distance of the region of interest with respect to the focal point of the X-ray tube is determined from the amount of movement x of the sample table necessary to prevent the position of the region of interest in the field of view of the X-ray detector from changing and the tilt angle θ by the tilt mechanism. It is characterized by including a calculating step .

According to the present invention, when a spatial calibration value is obtained based on an arbitrary perspective magnification using a reference sample, the spatial calibration value is stored together with the perspective magnification, and the sample inside the fluoroscopic object is stored. the fluoroscopic magnification of the distance is unknown attention site from the table surface, necessary for by tilting the X-ray detector by tilting mechanism, does not change the position of the target sites in the field of view of the X-ray detector at its tilting back and forth Because it is equipped with a means to accurately determine the amount of movement and tilt angle of the sample table , once it is spatially calibrated based on an arbitrary perspective magnification, it exists at an arbitrary height within the fluoroscopic object. By accurately determining the perspective magnification of the target area to be updated, the spatial calibration value is automatically updated in accordance with the perspective magnification ratio, and the actual size of the target area can be easily determined from the screen using a measurement bar tool or the like. Can be measured accurately To become.

  The present invention is applied to an X-ray fluoroscopic apparatus equipped with an X-ray detector tilting mechanism, and the X-ray detector is tilted by the tilting mechanism, and the sample table is offset by the tilting so as to cancel the movement of the region of interest on the screen. And an apparatus for calculating the distance from the focal point of the X-ray tube at the site of interest inside the fluoroscopic object from the tilt angle of the X-ray detector and the amount of movement of the sample table.

Figure 1 is a block diagram illustrating the principal components of a real施例of the present invention, is a view showing shown together with a block diagram illustrating a schematic electrical configuration representing the mechanical structure.

  The X-ray tube 1 is disposed such that the optical axis L of the X-ray is directed upward in the vertical direction, and a sample table 2 along a horizontal plane is provided above the X-ray tube 1. An X-ray camera 3 is disposed above the sample table 2 with a gap between them, and the fluoroscopic object W (hereinafter referred to as the sample W) is placed on the sample table 2 from below X. The X-rays irradiated with the rays and transmitted through the sample W enter the X-ray camera 3. The X-ray camera 3 is, for example, a publicly known combination of an image intensifier and a CCD. The output of the X-ray camera 3 is taken into a computer 4 on which a capture board is installed, and the sample 5 is X-rayed through the display 5. An image is displayed.

  The X-ray camera 3 can be tilted at an arbitrary angle θ with respect to the X-ray optical axis L by the tilt mechanism 6. As shown in the figure, when the z-axis is taken in the vertical direction and the x and y axes are taken in the directions orthogonal to each other on the horizontal plane, the X-ray camera 3 moves the X-ray tube 1 on the xz plane. This is performed by an arc-shaped motion centered on the focal point 1a.

  The sample table 2 can be moved in the x-, y-, and z-axis directions by the x-axis drive mechanism 2a, the y-axis drive mechanism 2b, and the z-axis drive mechanism 2c. The x-axis drive mechanism 2a, the y-axis drive mechanism 2b, the z-axis drive mechanism 2c, and the tilt mechanism 6 are driven by motors corresponding to the x-axis drive mechanism 2a, the y-axis drive mechanism 2b, and the tilt mechanism 6, respectively. The drive is controlled by the supplied drive signal. The axis control device 7 is connected to the computer 4 described above, and the sample table 2 can be moved in an arbitrary three-dimensional direction by operating a keyboard 4a or a joystick (not shown) of the computer 4. . Further, the coordinates of the sample table 2 in the x, y, and z axis directions can be recognized by the computer 4 by the output of, for example, an encoder provided for each axis.

  The computer 4 designates an arbitrary region of interest V on a calibration program for spatial calibration and an X-ray fluoroscopic image of the sample W displayed on the display 5, whereby the surface of the sample table 2 of the region of interest V is displayed. Automatically calculates the distance from the image to calculate the exact perspective magnification, updates the spatial calibration value automatically at the time of calculation, and uses the updated spatial calibration value to change any 2 A measurement program for obtaining the distance between points is written.

  In the calibration program, as shown in a flowchart showing the procedure in FIG. 2, a required reference sample such as a microchart is set at a predetermined position on the sample table 2, and the reference table is moved by moving the sample table 2. In the field of view of the X-ray camera 3, the fluoroscopic image is displayed on the screen of the display 5, and a command for spatial calibration is input from the keyboard 4 a or the like. As a result, the measurement bar tool is displayed on the screen. The operator operates the mouse 4b to move and expand / contract the measurement bar tool so that it passes between two known points of the actual size of the reference sample, and then inputs the actual size from the keyboard 4b. From the measurement bar tool length and actual dimension, the actual dimension per pixel of the screen is calculated as a spatial calibration value C and stored in the memory of the computer 4.

  At this time, the reference sample is set at a predetermined position on the sample table so that the distance from the surface of the sample table 2 becomes constant, and the reference surface of the X-ray camera 3 Since the distance from the focal point 1a of the X-ray tube 1 is known, the position in the z direction of the sample table 2 at the time of spatial calibration, and the imaging magnification and display on the image receiving surface of the X-ray camera 3 which are apparatus constants In addition to the relationship with the size of the fluoroscopic image displayed on the screen of the device 5, an accurate fluoroscopic magnification (total magnification) M can be calculated. In addition, it is stored in the memory of the computer 4.

  On the other hand, in the measurement program, as shown in the flowchart showing the procedure in FIG. 3, the fluoroscopic object W is placed in the field of view without tilting the X-ray camera 3 (tilt angle θ = 0), and the fluoroscopic object. In a state where a fluoroscopic image of the object W is displayed on the display device 5, an arbitrary target region V is designated on the screen. The mutual relationship between the X-ray tube 1, the sample table 2, and the X-ray camera 3 in this state is as shown in FIG.

By performing the above designation, the tilt mechanism 6 tilts by a preset angle at a preset angular velocity. By this tilting, the field of view of the X-ray camera 3 moves and the position of the attention site V changes on the screen. In this program, the attention site V is positioned at the initial position on the screen. The sample table 2 is automatically moved in the x-axis direction for tracking. As shown in FIG. 4 (B), when the tilt angle theta has reached a preset theta _c, when the sample table 2 has been moved by x _c, using the theta _c and x _c, of interest The distance h from the surface of the sample table 2 of the part V is calculated based on the following formula.
h = x _c / tan θ _c (1)

  As described above, the distance between the image receiving surface of the X-ray camera 3 and the focal point 1a of the X-ray tube 1 is known, and the distance between the surface of the sample table 2 and the focal point 1a of the X-ray tube 1 is also an encoder. Therefore, when h is known, an accurate perspective magnification (total magnification) m of the site of interest V can be calculated in the same manner as in spatial calibration using a reference sample. .

When the perspective magnification m of the attention site V is calculated in this way, the perspective magnification M stored at the time of spatial calibration is updated to m, and at the same time, the perspective magnification M and the attention site V obtained at the time of spatial calibration are updated. And the ratio m / M of the two is used to update the spatial calibration value C stored at that time to a new spatial calibration value Cr by the following equation.
Cr = C · m / M (2)

  After the above update operation is completed, the measurement bar tool is displayed, and the actual dimension between the two points is displayed by moving / stretching the measurement bar tool between any two points of the target region V by the same procedure as before. Is measured using the updated spatial calibration value Cr, and the measurement result is displayed on the display 5.

  With the above operation, the distance between any two points in the site of interest V whose distance in the z direction from the surface of the sample table 2 is unknown can be determined easily and with high accuracy.

It is a principal part block diagram of the Example of this invention, and is the figure which writes together and shows the schematic diagram showing a mechanical structure, and the block diagram showing an electric structure. It is a flowchart which shows the content of the calibration program in the Example of this invention. It is a flowchart which shows the content of the measurement program in the Example of this invention. It is explanatory drawing at the time of calculating the fluoroscopy magnification of the attention site V with the measurement program in the example of the present invention.

Explanation of symbols

1 X-ray tube 2 Sample table 3 X-ray camera 4 Computer 5 Display 6 Tilt mechanism 7 Axis control device W Sample V Target region

Claims (1)

And X-ray tube, a sample table having a moving function of the three-dimensional directions, the X-ray detector disposed facing the X-ray tube across the sample table, the X-ray that the X-ray detector A tilting mechanism for tilting about the focal point of the tube ; an image forming means for displaying an X-ray fluoroscopic image based on pixel information from the X-ray detector on the display; and an X-ray optical axis direction with respect to the surface of the sample table In the X-ray fluoroscopic apparatus for precision measurement provided with a spatial calibration value calculating means for calculating a spatial calibration value from an X-ray fluoroscopic image of a reference sample of a known size placed at a position where the distance to is known,
Storage means for storing the spatial calibration value together with the fluoroscopic magnification of the X-ray fluoroscopic image of the reference sample used for calculation of the spatial calibration value, and the distance from the surface of the sample table exists at an unknown position includes a site of interest perspective enlargement ratio calculation means for exiting calculate the perspective magnification region of interest of the object of fluoroscopy, when calculating the perspective magnification attention site by the attention site fluoroscopic magnification ratio calculating means, the calculated value and the stored The spatial calibration value is automatically changed based on the ratio with the perspective magnification stored in the means, and the spatial calibration value after the change and the calculated perspective magnification of the target region A spatial calibration value / perspective magnification update means for updating contents is provided, and when the X-ray detector is tilted by a predetermined angle by the tilt mechanism, the attention site fluoroscopic magnification calculation means is before and after the tilt. X A step of calculating the distance of the site of interest with respect to the focal point of the X-ray tube from the amount x of movement of the sample table necessary for not changing the position of the site of interest in the field of view of the detector and the tilt angle θ by the tilt mechanism. X-ray fluoroscopic apparatus for precision measurement, characterized by comprising:

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